Ahead of directly manages a country by making decisions and wielding power.
a. government
b. monarchy
c. theocracy
d. state

A head of a state is the head of the state that represents the country in official situations: but this is a representative function rather than a function with actual power. 

Similarly, head of a monarchy: a monarch could be only a representative function. the correct answer is : the head of a government: this person has the actual power to make decisions.